linux-kernel - Re: [PATCH 1/2] dw_dmac: store direction in the custom channel structure

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Date:	Tue, 20 Nov 2012 19:38:57 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	spear-devel <spear-devel@...t.st.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dw_dmac: store direction in the custom channel structure

On 20 November 2012 19:08, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> Currently the direction value is come from the generic slave configuration

s/is come/comes

> structure and explicitly as a preparation function parameter. The first one is
> kinda obsoleted. Thus, we have to store the value passed to the preparation
> function somewhere in our structures to be able to use it later. The best
> candidate to provide the storage is a custom channel structure. Until now we
> still keep and check the direction field of the slave config structure as well.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  drivers/dma/dw_dmac.c      |   10 ++++++++--
>  drivers/dma/dw_dmac_regs.h |    2 ++
>  2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
> index 5e2c4dc..58c6d3c 100644
> --- a/drivers/dma/dw_dmac.c
> +++ b/drivers/dma/dw_dmac.c
> @@ -178,9 +178,9 @@ static void dwc_initialize(struct dw_dma_chan *dwc)
>                 cfghi = dws->cfg_hi;
>                 cfglo |= dws->cfg_lo & ~DWC_CFGL_CH_PRIOR_MASK;
>         } else {
> -               if (dwc->dma_sconfig.direction == DMA_MEM_TO_DEV)
> +               if (dwc->direction == DMA_MEM_TO_DEV)
>                         cfghi = DWC_CFGH_DST_PER(dwc->dma_sconfig.slave_id);
> -               else if (dwc->dma_sconfig.direction == DMA_DEV_TO_MEM)
> +               else if (dwc->direction == DMA_DEV_TO_MEM)
>                         cfghi = DWC_CFGH_SRC_PER(dwc->dma_sconfig.slave_id);
>         }

I have a doubt here. This routine is called both for memcpy and slave transfers.
Earlier if (dws), code was used to check slave/non-slave transfer but with your
earlier patch, for if (!dws) case too, there can be slave transfers
based on direction.

Consider a situation. A channel is used for slave transfers and have
direction set
to DMA_DEV_TO_MEM. Now, channel is freed and used for memcpy. Now the
direction value is retained as we haven't updated it. So, is this a
potential bug?

> @@ -807,6 +807,8 @@ dwc_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>         if (unlikely(!dws || !sg_len))
>                 return NULL;
>
> +       dwc->direction = direction;
> +
>         prev = first = NULL;
>
>         switch (direction) {
> @@ -983,6 +985,7 @@ set_runtime_config(struct dma_chan *chan, struct dma_slave_config *sconfig)
>                 return -EINVAL;
>
>         memcpy(&dwc->dma_sconfig, sconfig, sizeof(*sconfig));
> +       dwc->direction = sconfig->direction;
>
>         convert_burst(&dwc->dma_sconfig.src_maxburst);
>         convert_burst(&dwc->dma_sconfig.dst_maxburst);
> @@ -1339,6 +1342,8 @@ struct dw_cyclic_desc *dw_dma_cyclic_prep(struct dma_chan *chan,
>         if (unlikely(!is_slave_xfer(direction)))
>                 goto out_err;
>
> +       dwc->direction = direction;
> +
>         if (direction == DMA_MEM_TO_DEV)
>                 reg_width = __ffs(sconfig->dst_addr_width);
>         else
> @@ -1713,6 +1718,7 @@ static int __devinit dw_probe(struct platform_device *pdev)
>                 channel_clear_bit(dw, CH_EN, dwc->mask);
>
>                 dwc->dw = dw;
> +               dwc->direction = DMA_TRANS_NONE;
>
>                 /* hardware configuration */
>                 if (autocfg) {
> diff --git a/drivers/dma/dw_dmac_regs.h b/drivers/dma/dw_dmac_regs.h
> index 8881e9b..362aba1 100644
> --- a/drivers/dma/dw_dmac_regs.h
> +++ b/drivers/dma/dw_dmac_regs.h
> @@ -9,6 +9,7 @@
>   * published by the Free Software Foundation.
>   */
>
> +#include <linux/dmaengine.h>
>  #include <linux/dw_dmac.h>
>
>  #define DW_DMA_MAX_NR_CHANNELS 8
> @@ -188,6 +189,7 @@ struct dw_dma_chan {
>         void __iomem            *ch_regs;
>         u8                      mask;
>         u8                      priority;
> +       enum dma_transfer_direction direction;
>         bool                    paused;
>         bool                    initialized;

better align it with tabs and update earlier ones too with extra tabs.

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
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